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https://www.theatlantic.com/science/archive/2020/10/what-does-cerebellum-really-do/616689/

The earliest experiments with the cerebellum—Latin for “little brain”—date back centuries. Those investigations weren’t pretty: Scientists simply lopped off the structure from live animals, then observed their behavior. For example, the 19th-century French physiologist Marie-Jean-Pierre Flourens conducted cerebellectomies on pigeons and reported that the animals started to teeter and totter as if intoxicated. These findings led him to propose that the structure was necessary for coordinating motion. Clinical observations of people with cerebellar injuries later confirmed this hypothesis, cementing the cerebellum’s reputation for nearly two centuries as a movement-coordination structure.

It turns out the cerebellum plays a significant role in judgment and planning and we wouldn't be intelligent without it.